1. Field of the Invention
This invention relates to an improvement in rocket nozzles, and more particularly, to a non-radiating plural position flexible auxiliary nozzle portion or exit cone for a rocket motor.
2. Description of the Prior Art
Deep space ballistic missile systems or satellite probes require high performance, low weight, and highly packageable primary propulsion systems. Excluding propellant tanks, the largest component of a propulsion system is the rocket exhaust nozzle. The rocket nozzle takes up a great deal of valuable space relative to its mass.
Conventional thrust nozzle exit cones for rocket motor ballistic systems are designed to provide the best average performance over the whole intended trajectory within the volumetric constraints created by launch tube clearance and interstage length limitations. One of the functions of the exit cone of a rocket nozzle is to provide an inclined surface against which the expanding exhaust plume of the rocket can bear, thereby providing some of the forward thrust of the rocket. The exhaust plume grows larger with increasing altitude of the rocket because of the decreasing pressure of the ambient atmosphere. As a result, in a conventional rocket nozzle, the exhaust plume at low altitudes is too small for the available surface of the exit cone. This allows the formation, inside the edges of the exit cone, of a partial vacuum which creates an atmospheric drag on the rocket. At high altitudes the exhaust plume is too large for the exit cone, and as a result, much of the potential energy is unused. A rocket nozzle that is sufficiently large to make full use of the expanding exhaust gases of a rocket in the low ambient pressures at high altitudes would normally occupy an inordinately large proportion of the available storage space in silos, submarines, aircraft, or between stages of a multistage missile.
Various proposals have been made in the prior art to provide a large expansion ratio nozzle that can be stowed in a collapsed or retracted configuration and thus made to fit into a minimal storage space, and that can be extended to the operating position after motor ignition. These have included the use of: an inflatable auxiliary rocket nozzle portion or exit cone as disclosed in U.S. Pat. No. 3,596,465 to Thomas O. Paine et al; rocket nozzle exit cones that are flexible and can be expanded or compressed in various ways as disclosed in said Paine et al patent, and in U.S. Pat. No. 3,358,933 to J. H. Altseimer, U.S. Pat. No. 3,711,027 to Lee F. Carey, and U.S. Pat. No. 3,784,109 to John W. Dueringer; and rocket nozzle exit cones that are segmented longitudinally as disclosed in a paper entitled "Nested Extendible Exit Cone Solid Rocket Nozzle Engineering Evaluation Program" presented at the AIAA/SAE 14th Joint Propulsion Conference, Las Vegas, Nev., July 25-27, 1978, and as disclosed in copending application for U.S. Patent bearing Ser. No. 230,939, filed on Feb. 12, 1981 by Frank S. Inman, one of the present inventors, and assigned to Thiokol Corporation, the assignee of the present invention.
In FIGS. 1-4 of the Altseimer patent a rocket nozzle skirt is provided that is expandable transversely of the rocket motor longitudinal axis, the skirt being said to be made of metallic or non-metallic material, but not being foldable. In FIG. 5 a foldable flared skirt is provided. This skirt is said to be made of material such as reinforced rubber produced under the trademark GEN-GARD by the General Tire and Rubber Company or asbestos reinforced with inconel wire and impregnated with an ablative material such as Teflon.
The paine et al patent shows a skirt for a rocket engine that is made of a three-dimensional metal fabric. The outer surface of the metal fabric is said to be sealed with a silicon elastomer, and the fabric is described as being cooled by exhaust gas from a main rocket turbine.
In the specification of the Paine et al patent, mention is made of extendible nozzle skirts having been developed in the prior art using an elastomeric ablator supported by a woven textile fabric, the patentees noting further that due to the thickness of the ablator required for cooling the textile fabric and for resisting the temperature and erosion of the exhaust gases, the ablator becomes extremely heavy and this offsets any gains in engine performance.
The Carey and Dueringer patents disclose related subject matter, the material of the foldable rocket nozzle extension of the Carey patent being described as sheet metal but that of the Dueringer patent not being mentioned.
An additional requirement for deep space satellite probes is that thermally sensitive gear, for example, reaction control system hardware, radioactive thermal generator batteries, data recorders, and navigational equipment be protected from the rocket nozzle external surface radiation during its operation.
While the prior art proposals mentioned above are concerned with the problem of how to make the auxiliary nozzle portion or exit cone of a rocket nozzle more compact so as to fit in a minimal storage space, none of them have disclosed, or otherwise taught or considered, how to make the rocket nozzle cone collapsible or retractable, and, at the same time, shown how to insulate it to make its external surface non-radiating while maintaining its flexibility. The metallic exit cones proposed in the prior art do not have the required non-radiating surface characteristics, nor do the prior art exit cones made of an elastomeric ablator supported by a woven, textile fabric, the reinforced rubber, or the wire reinforced asbestos sheet impregnated with Teflon.